Scientific Method: Variables (Part 1)

Change variable, dependent variable, control variables

1. Part 1 SCIENTIFIC METHOD: Variables By Moira Whitehouse PhD Modified by Chele Burch for 5th Grade 8/6/18

2. How do scientists conduct experiments?

3. Answer: They use the scientific method.

4. The scientific method is a procedure scientists use to answer specific questions.

5. The number 1 purpose of using the scientific method is to make sure the experiment is fair .

6. What does a fair experiment look like? Decide if the following experiment is fair …

7. Professor William Wonka wonders if a new formula for plant growth will make plants grow faster.

8. He decides to grow 2 plants and feed one of them his special plant food. So, he buys a hibiscus plant and a bamboo plant.

9. He measures the height of each plant.

10. He places the hibiscus on a counter in front of his kitchen window. He places the bamboo on his bedroom dresser.

11. Every other day, he pours a little water mixed with his plant food in the hibiscus plant. And, every other day, he pours a little water (without the plant food) in the bamboo plant.

12. After 4 weeks, he measures the height of each plant again.

13. He observes that the hibiscus plant grew 2 inches taller, while the bamboo plant only grew half an inch taller. 2 inches ½ inch

14. So, Professor William Wonka concludes that his plant food does, in fact, help plants to grow faster.

15. Is Professor William Wonka correct? How do you know?

16. Directions: Discuss this question with your team mates. You may use scratch paper to help you brainstorm.

17. Is the professor correct? The answer is ….

18. … Not exactly.

19. The professor’s experiment wasn’t fair. He can’t be sure that it was the plant food that made the hibiscus plant grow faster than the bamboo, and not some other factors.

20. To conduct a fair science experiment, one must pay attention to the variables .

21. Consider the following …

22. You want to design a car that will roll down a ramp really fast. ramp

23. So, you need to know what things affect how fast a car will roll down a ramp. ramp

24. What could you do to the car or ramp to make the car go faster? ramp

25. Did you come up with making the ramp steeper? How about making the car heavier? Also, you could grease the wheels to make them spin more easily. Can you think of any other things you could change to make the car faster?

26. All of the things you could change to make the car go faster are called...

27. Variables!

28. There are 3 main kinds of variables:

29. There are 3 main kinds of variables: 1. The change variable

30. There are 3 main kinds of variables: 1. The change variable 2. The dependent variable

31. There are 3 main kinds of variables: 1. The change variable 2. The dependent variable 3. The control variables

32. Let’s look more closely at these 3 kinds of variables.

33. The 1 st type of variable is: 1. The change variable

34. 1. The change variable is: • the only thing in the experiment that isn’t kept the same. • also known as the independent variable.

35. Important!!! • There can only be 1 change variable in any experiment!!!!

36. In the experiment on the next slide, identify the change variable. What is the 1 thing that isn’t the same with plant 1, 2, and 3?

37. No Water Plant 1 Plant 2 Plant 3 20 mL Water every day 40 mL Water every day

38. You are correct if you said the change variable is the amount of water each plant receives.

39. The 2nd type of variable is: 2. The dependent variable

40. 2. The dependent variable is • What you measure or observe to see how the change variable affects the experiment.

41. In our 3 plants/water experiment, what could be some dependent variables? (What could the experimenter observe or measure to see if the amount of water made a difference to the health of each plant?)

42. No Water Plant 1 Plant 2 Plant 3 20 mL Water every day 40 mL Water every day

43. The experimenter could have, for example, counted the number of green leaves on each plant. So, the number of leaves is a dependent variable.

44. He could also have measured the height of the plants after 14 days. So, plant height could be another dependent variable.

45. Here are some examples of dependent variables in other experiments:

46. Dependent Variable: ...the amount of water absorbed by two different brands of paper towels...

47. Dependent Variable: ...how far a ball rolls from different ramp angles...

48. Dependent Variable: ...and the amount of bird food eaten at a bird feeder when the type of bird food is changed.

49. Whenever possible the experimenter should measure , instead of just observe, the dependent variable.

50. In order to measure the dependent variable, the experimenter uses tools such as...

51. ...a metric ruler or meter stick to measure how far something moved...

52. ...a balance scale to measure the mass of something...

53. ...and a thermometer to measure how hot or cold something is.

54. What might the change variable be in this experiment on water evaporating? without fan with fan that moves the air

55. What could be the dependent variable in this experiment? Remember you should measure. without fan with fan that moves the air

56. What might the change variable be in this experiment on keeping water hot? PLASTIC CUP OF HOT WATER STYROFOAM CUP OF HOT WATER

57. What might be the dependent variable in this experiment? Remember you should measure. PLASTIC CUP OF HOT WATER STYROFOAM CUP OF HOT WATER

58. What would the change variable be in this experiment on how much heat different soils absorb?

59. What could be the dependent variable in this experiment? Remember, you should measure.

60. Now, you have an understanding of what a change variable and dependent variable are, but there is 1 more type of variable...

61. The 3 rd type of variable is 3. The control variables

62. Control variables are all those things in an experiment that you keep the same.

63. Unlike a change variable, there can be many control variables in an experiment.

64. Think back to our experiment with the 3 plants and amount of water. What are the control variables? (What should be kept the same?)

65. No Water Plant 1 Plant 2 Plant 3 20 mL Water every day 40 mL Water every day

66. The control variables could include: the amount of sunlight the temperature of the air the kind of soil the size of the pot

67. What would be the problem if we changed both the amount of water and the type of soil the plant is growing in at the same time?

68. Answer: You wouldn’t know if the growth was due to the water or the type of soil.

69. Plant 3 Plant 1 Plant 2 20 mL Water every day No Water 40 mL Water every day Sandy soil Clay soil Potting soil

70. Let’s review …

71. In order to make correct conclusions when doing experiments we must: • have only ONE change variable. • keep EVERYTHING else the same.

72. You want to find out if making the angle of the ramp higher would make the car coast farther . So let’s look at that toy car on the ramp again. So your question is: Will increasing the angle of the ramp make my car roll farther?

73. • What would your change variable be?

74. • What would your dependent variable be?

75. •What would some of your control variables be?

76. Control variables? What’s wrong with this picture? MADE OF PLASTIC MADE OF WOOD

77. MADE OF PLASTIC MADE OF PLASTIC ANY PROBLEM HERE?

78. Think you have it! To use the scientific method to solve a problem, you set up an experiment to answer the question: What is the affect of the change variable on the dependent variable?

79. What is a change variable?

80. What is a change variable? A change variable is the only thing that is different in an experiment.

81. What is a dependent variable?

82. What is a dependent variable? A dependent variable is what you measure or observe to determine how the change variable affected the experiment.

83. What are control variables?

84. What are control variables? Control variables are the things that must be kept the same .

85. Good job!

86. On the left side page of your science notebook, create a one-pager that demonstrates what you know about change variables, dependent variables, and control variables. You will be graded on this.